Abstract: A novel apparatus is disclosed which comprises: (a) pumping means for injecting a fluid through a conduit means into an inlet pipe of a fluid mixing tank, (b) said fluid mixing tank comprising a plurality of compartments connected in series and in fluid communication with adjacent compartments in the series, and designed to provide for a horizontal flow of fluids from the first compartment to the last compartment in the series, (c) at least one compartment being equipped with one or more radial-flow impellers connected to a vertical shaft, and means for rotating such impellers at a rate designed to stir the contents of the compartment radially with high shear and prevent fluid stagnation, (d) at least one compartment being equipped with one or more axial flow impellers connected to a vertical shaft, and means for rotating such impellers at a rate designed to circulate the contents of the compartment vertically, (e) the inlet pipe being designed to introduce fluids into the first compartment, and (f) a means